The present invention relates to fluid controllers for use in vehicle steering systems, and more particularly, to such controllers which are to be used with unequal area steering cylinders.
There are now a number of vehicles which utilize full fluid linked steering systems, including fluid controllers of the type to which the present invention relates, wherein it is considered desirable to utilize unequal area steering cylinders. An unequal area cylinder is one having only a single rod extending from the cylinder, such that the cylinder has a "rod end" having a particular cross-sectional area subject to fluid pressure ("flow area"), and a "head end" having a relatively larger cross-sectional area ("flow area"). In many vehicle applications, the use of unequal area of cylinders is desirable because the linkage arrangement and overall installation is simplified, and therefore, less expensive than is the case for a double rod end cylinder.
In a typical fluid controller of the type to which the present invention relates, the fluid flow output from the controller is the same in either direction, assuming equal steering wheel rotation, for reasons which are well understood by those skilled in the art. Unfortunately, this characteristic of fluid controllers has limited their usefulness with unequal area cylinders. When the prior art fluid controller is used with an unequal area cylinder, the result is that the operator experiences a different number of turns lock-to-lock in one direction than in the other. Such an arrangement is generally considered unacceptable to the vehicle manufacturers, because most operators prefer that the vehicle move in a straight line when the steering wheel is in its centered position, and having a different number of turns lock-to-lock will eliminate the desired registry between the steered wheels and the steering wheel.